Simultaneous extraction and recovery of uranium and vanadium from wet process acids

ABSTRACT

A process for the simultaneous coextraction of uranium and vanadium from an aqueous acidic solution containing the same comprising contacting said aqueous acidic solution with an organic phase comprising a mixture of (a) an alkyl substituted diaryl phosphoric acid, (b) a trialkylphosphine oxide compound, and (c) an organic diluent whereby the uranium and vanadium are coextracted into the organic phase and thereafter recovering the uranium and vanadium from the organic phase.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of applicants' copendingapplication Ser. No. 720,995 filed Sept. 7, 1976 now abandoned entitled"Simultaneous Extraction and Recovery of Uranium and Vanadium from WetProcess Acids."

BACKGROUND OF THE INVENTION

Phosphoric acid generally is produced commercially by one of twomethods. One method generally is called the "furnace" method, and theother generally is referred to as the "wet process" method. In the wetprocess method of producing phosphoric acid, phosphate rock is contactedwith a mineral acid such as sulfuric acid. Most phosphate rock containsmetal compounds in varying amounts. In many cases, these metal compoundsare dissolved from the phosphate rock and appear in the wet process acidas contaminants. Vanadium and uranium compounds are among thosedissolved from the phosphate rock, particularly when the rock is fromthe so-called western deposits of Idaho, Wyoming, Utah and Montana.

Vanadium, however, is an undesirable component of wet process phosphoricacid in that it prevents the use of the phosphoric acid in making animalfeed supplements, as the amount of vanadium must be kept at a low levelin such animal feed supplements. Similarly, uranium is undesirable insuch feed supplements.

On the other hand, vanadium and uranium are valuable materials and wetprocess phosphoric acid can be an important source of these materials.Therefore, a process for the simultaneous recovery of vanadium anduranium from wet process phosphoric acid provides an important benefit,in that the vanadium and uranium are converted from undesirablecontaminants to valuable by-products.

BRIEF DESCRIPTION OF THE PRIOR ART

There have been many attempts made in the past to recover vanadium fromwet process acid. One such process involves addition of a solubleferrocyanide compound to the acid to precipitate the vanadium, asdescribed more fully in U.S. Pat. No. 1,544,911. Other such processesinvolve extraction of the acid with an organic extractant for thevanadium. U.S. Pat. No. 2,211,119 describes a process in which thepreferred organic extractant is isopropyl ether. U.S. Pat. No. 3,437,454describes a process in which the preferred organic extractant is analphahydroxy oxime. In U.S. Pat. No. 3,700,415, assigned to the sameassignee as the present invention, there is described a process forextracting vanadium from wet process phosphoric acid utilizing certainneutral organophosphorus compounds as an extractant.

Further, there have been several processes developed for recoveringuranium from wet process acids derived from eastern phosphate deposits.Typical of such uranium recovery processes are those disclosed in U.S.Pat. Nos. 2,859,094, 3,052,514 and 3,243,257 using, as an extractant, amixture of a dialkyl phosphoric acid and a neutral organophosphoruscompound.

Furthermore, in U.S. Pat. No. 3,836,476, assigned to the same assigneeas the present invention, there is described a process for thesimultaneous coextraction of uranium and vanadium from wet processphosphoric acid utilizing, as an extractant, a mixture of dialkylphosphoric acid, trialkylphosphine oxide and an organic diluent. Thatprocess has resulted in the successful coextraction of up toapproximately 82 percent of the vanadium and approximately 88 percent ofthe uranium present in the wet process acid.

SUMMARY OF THE INVENTION

It has now been discovered that an organic solvent comprising a mixtureof (a) an alkyl substituted diaryl phosphoric acid, (b) atrialkylphosphine oxide compound and (c) an organic diluent willeffectively coextract up to approximately 99 percent of the uranium andapproximately 85 percent of the vanadium present in wet process acidswhile utilizing extractant concentrations lower than heretoforepossible. This improved extraction capability results in a significantlylower volume of solvent required to effect uranium and vanadium recoveryfrom wet process acids. Thus, the new extractant composition provides amore economical process in that (1) smaller processing equipment isrequired; (2) smaller solvent inventories are required and (3) lowerextractant concentrations can be used to effect the recovery operations.

In addition, the process of the present invention has been found toremove certain other impurities from wet process phosphoric acid. Theseinclude yttrium, iron, zinc, bromine and possibly trace amounts of othermetallic components. This purification is seen as a valuble side effectof the present process and provides the additional benefit of allowingthe recovery of other by products of economic worth such as yttrium.

Broadly, the present invention provides a process for the simultaneouscoextraction of uranium and vanadium for acidic solutions. In practicingthe process, the aqueous acidic solution containing uranium and vanadiumvalues first is treated with an oxidant to oxidize the uranium to thehexavalent oxidation state(VI) and the vanadium to the pentavalentoxidation state(V).

The oxidized aqueous acidic solution then is contacted with an organicsolvent comprising a mixture of (a) an alkyl substituted diarylphosphoric acid, (b) a trialkylphosphine oxide compound and (c) anorganic diluent. The molar ratio of alkyl substituted diaryl phosphoricacid to trialkylphosphine oxide compound is within the range of fromabout 1:10 to about 1.5:1, with a preferred range of from about 1:8 toabout 1:1 and an especially preferred range of from about 1:3 to about4:5. It has been found that by utilizing such ratios, substantialquantities of uranium and vanadium are coextracted into the organicphase.

The loaded organic phase subsequently is separated from the aqueousphase. Thereafter, the uranium and vanadium are stripped from the loadedorganic phase with, for example, solutions of an aqueous base orreducing agents.

According to a preferred embodiment, the vanadium is preferentiallystripped from the loaded organic phase utilizing a base such as, forexample, sodium hydroxide, and controlling the addition of the strippingsolution so that the equilibrium pH is about 5.5. Subsequently, theuranium can be stripped from the organic phase by an aqueous basicsolution such as sodium carbonate or ammonium carbonate, for example, orby a reducing agent such as ferrous iron dissolved in phosphoric acid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, a process is provided for thecoextraction of uranium and vanadium from an aqueous acidic solutioncontaining the same utilizing a solvent comprising a mixture ofcomplexing agents (a trialkylphosphine oxide compound and an alkylsubstituted diaryl phosphoric acid) and an organic diluent.

The trialkylphosphine oxide compounds of this invention have thefollowing general formula: ##STR1## where R, R' and R" each are organicsaturated hydrocarbon radicals containing from 4 to 14 carbons. Mixturesof compounds having the general formula as defined above also may beused.

Exemplary alkyl radicals of the above formula are the butyl, amyl, hexyland octyl radicals.

In addition to the tertiary phosphine oxides, it is to be understoodthat within the scope of the claimed invention the corresponding oxoniumsalts are also contemplated. As examples of such oxonium salts may bementioned tri-n-octylphosphinoxonium bisulfate,tri-n-octylphosphinoxonium phosphate and tri-n-butylphosphinoxoniumnitrate. These salts are typically prepared by contacting an organicsolution of a phosphine oxide with an aqueous solution of theappropriate acid.

According to a preferred embodiment of the present invention, thetrialkylphosphine oxide compounds are those wherein R, R' and R" arealkyl radicals of from 6 to 12 carbon atoms.

An especially preferred trialkylphosphine oxide compound according tothe present invention is tri-n-octylphosphine oxide.

The alkyl substituted diaryl phosphoric acids applicable to the instantinvention are represented by the general formula: ##STR2## where R₁ andR₂ represent aryl radicals, at least one of which is substituted with analkyl group, and the total number of carbon atoms contained in the alkylsubstituted diaryl phosphoric acid is at least 13. Examples ofapplicable alkylaryl groups include 2-ethylhexylphenyl, n-octylphenyl,pentylphenyl, hexylphenyl, heptylphenyl, nonylphenyl, dodecylphenyl andthe like.

A preferred group of alkyl substituted diaryl phosphoric acids are thosecontaining from about 16 to 36 carbon atoms. Examples of such acidsinclude butylphenyl-phenyl phosphoric acid, butylphenyl-octylphenylphosphoric acid, didodecylphenyl phosphoric acid and dioctyphenylphosphoric acid. An especially preferred acid is dioctylphenylphosphoric acid.

In accordance with the present process, the trialkylphosphine oxidecompound and the alkyl substituted diaryl phosphoric acid are dissolvedin a water-immiscible organic solution containing the uranium andvanadium. The term "water-immiscible organic diluent" as used hereinrefers to an organic material normally liquid at ambient temperatureswhich may be substantially, but not necessarily entirely, insoluble inwater. The preferred organic diluents for the process of the presentinvention are hydrocarbons. Examples of suitable hydrocarbon solventsinclude isooctane, kerosene, and the like. Solvents which containfunctional groups can also be employed providing that the functionalgroups do not adversely affect the extraction. Particularly good resultsare obtainable when the organic diluent is a substantially nonreducingdiluent with respect to oxidation by the vanadium(V) present.

The amount of organic extractant phase to be used for most efficientextraction is from about 0.15 to about 10 times the volume of acidsolution to be treated. Particularly good results have been obtainedwith an organic to aqueous ratio of from about 0.5:1 to about 1.5:1. Theratio of organic phase to aqueous acid phase to be used is dependentupon the concentration of extractants in the organic phase, thetemperature at which the extraction is performed, the contact timebetween the two phases and the amount of vanadium(V) in the acidsolution. The concentration of trialkylphosphine oxide in the organicphase may range from about 0.05 molar to about its limit of solubilityin the particular diluent employed, which limit is generally about 0.5molar to about 1.0 molar. An especially preferred range oftrialkylphosphine oxide concentration is from about 0.1 to about 0.5molar. The amount of alkyl substituted diaryl phosphoric acid present inthe organic phase may be determined based on the desired ratio oftrialkylphosphine oxide compound to alkyl substituted diaryl phosphoricacid. The molar ratio of alkyl substituted diaryl phosphoric acid totrialkylphosphine oxide may vary from about 1:10 to about 1.5:1, theespecially preferred range being from about 1:3 to about 4:5.

The process of the present invention is applicable to any aqueous acidicsolution containing uranium and vanadium. The instant process isparticularly applicable to wet process phosphoric acid obtained from thewestern phosphate deposits which contain significant quantities of bothuranium and vanadium.

It has been found in the practice of this invention that fluoride mustbe present in the aqueous acidic solution in order for the complexingagents of the present invention to properly complex the vanadium(V).Although the exact theory of the complex is not known, it is believedthat the fluoride is complexed with vanadium(V) and the complexingagent. The amount of fluoride present in the mixture preferably is atleast about 0.25 moles per mole of vanadium present, although a largeexcess of fluoride does not harm the extraction. Fluoride is a naturalcomponent of wet process phosphoric acid and therefore wet processphosphoric acid is particularly suited to the extraction process of thepresent invention.

Prior to contacting the aqueous acidic solution with the organicextractant mixture, the aqueous solution is treated, if necessary, withan oxidizing agent to make certain that the vanadium contained thereinis in the pentavalent oxidation state(V) and the uranium is in thehexavalent oxidation state(VI). When the vanadium and uranium are notpresent as vanadium(V) and uranium(VI), the extraction process with thesolvent extractants of the present invention is not satisfactory asvanadium and uranium in the lower oxidation states do not form a complexwith the extractants contemplated in the scope of the invention.

The aqueous acidic solution may be oxidized by any known method such as,for example, with sodium chlorate, manganese dioxide, ozone, and thelike. The oxidizer should be added in an amount sufficient to provide atleast the stoichiometric requirements for oxidation of all the vanadiumto vanadium(V) and uranium to uranium(VI). When there are otheroxidizable species present in the aqueous acidic solution, such as arefound in wet process acid, for example, it is desirable to provide anexcess of the stoichiometric requirements of the oxidizer. This beingnecessary, of course, to insure that substantially all the uranium andvanadium values present are oxidized.

The process of the present invention may be practiced within atemperature range of from about 20° C. to about 80° C. with atemperature of about 35° C. to about 55° C. being preferred.

It has been found that the contact time between the organic phase andthe acid phase is an important variable to consider when extractingvanadium from acidic solutions. Longer contact times result in increasedvanadium extraction. In practice, contact times of from about 1 minuteto about 60 minutes are satisfactory with about 5 minutes to about 30minutes per contact being especially preferred at temperatures of fromabout 40° C. to about 50° C. The extraction may be performed on a batchbasis or a continuous basis, such as in a continuous countercurrentmulti-stage extraction system.

In the process of the present invention, the organic phase is contactedwith an aqueous acidic solution containing uranium and vanadium, atleast a major portion of the vanadium and uranium values being in thepentavalent and hexavalent oxidation states respectively, whereby theuranium and vanadium are simultaneously coextracted in the organicphase. The loaded organic phase may be stripped by conventional methods;for example, the loaded organic phase may be contacted with an aqueoussolution of sodium carbonate, ammonium carbonate or similar base at a pHabove about 8.4 to simultaneously strip both the vanadium and uraniumvalues contained therein.

According to a preferred embodiment of the invention, the vanadium canbe stripped from the organic extract phase, free from the uranium. Inthis embodiment the loaded organic phase is contacted with an aqueoussodium hydroxide, sodium carbonate or other suitable basic strippingsolution under carefully controlled conditions so that the equilibriumpH of the resulting mixture does not exceed about 6. However, theequilibrium pH may rise to about 8.4 without causing significantstripping of uranium. It has been discovered that by such control of theequilibrium pH that vanadium is preferentially stripped from the loadedorganic phase. Particularly good results have been obtained when theaddition of a stripping solution is controlled such that the equilibriumpH is from about 5.5 to about 6.0. Under such conditions, substantiallyall the vanadium is stripped from the loaded organic phase withnegligible amounts of uranium being removed. Thus, stripping with anaqueous sodium hydroxide or similar solution at a controlled pH resultsin the preferential removal of only the vanadium values. The remaininguranium loaded organic can be processed for the subsequent removal ofthe uranium values. For example, the uranium loaded organic phase can bestripped with an aqueous solution of sodium carbonate, ammoniumcarbonate or similar base at a pH above about 8.4.

Suitable aqueous base strip solutions may contain any one of a number ofalkali metal hydroxides, carbonates or mixtures thereof. Ammoniumhydroxide can be used but is not as desirable for stripping vanadium asthe alkali metal hydroxides or carbonates.

Alternatively, the uranium loaded organic phase can be stripped with anaqueous acidic solution of phosphoric acid or hydrofluoric acid. Apreferred form of aqueous acidic stripping is obtained through additionof a reducing agent to the acidic solution which is capable of reducinguranium to the tetravalent state.

In alternate embodiments, both the vanadium and uranium can be strippedfrom the organic extract phase by means of a reducing agent. Selectionof an appropriate reducing agent and process conditions provide a meansby which the vanadium and uranium can be simultaneously stripped fromthe loaded organic phase into the same aqueous medium or sequentiallyinto the same or different aqueous media.

In one alternate embodiment, vanadium and uranium are simultaneouslystripped from the loaded organic phase with a phosphoric acid solutioncontaining a reducing agent, such as ferrous iron, in such an amount soas to reduce the vanadium to a mixture of trivalent and tetravalentstates while reducing the uranium to the tetravalent state.

In another alternate embodiment, the amount of reducing agent iscontrolled such that only vanadium is reduced and stripped from theloaded organic phase and the uranium remains primarily in the hexavalentstate. To produce high concentrations of vanadium in the strippingsolution by this technique, it is desirable to wash the stripped organicphase in a counter-current fashion with the stripping medium makeupsolution prior to addition of the reducing agent to the solution.

In yet another alternate embodiment, vanadium can be selectivelystripped from the loaded organic phase through use of a reducing agentin an aqueous stripping solution which is not capable of complexingtetravalent uranium. Such non-complexing aqueous stripping solutionsinclude sulfuric acid and the like. When using ferrous iron as thereducing agent in the sulfuric acid stripping solution, the reductionand stripping of vanadium is essentially complete while virtually nouranium is stripped from the loaded organic phase. The uranium then canbe stripped by any of the previously described methods.

An additional means of selectively stripping vanadium from the loadedorganic phase is with strong nitric acid solutions, which may alsocontain additional nitrate salts. While it is not clearly understood, itis believed the selective stripping results from the high affinity ofthe alkylphosphine oxide component of the organic phase for nitric acid.

Stripping may be accomplished in a batch or continuous operation. Apreferred method utilized a multi-stage countercurrent strippingprocess.

The foregoing description and the following specific examples are forthe purpose of illustration and are not to be considered as limiting thescope of the invention, reference being had to the appended claims forthis purpose.

EXAMPLE I

This example demonstrates, in a one stage extraction, the effect ofvarying the molarity of the trialkylphosphine oxide compound and alkylsubstituted diaryl phosphoric acid in the organic phase as well as theeffect of varying the ratio of trialkylphosphine oxide compound to alkylsubstituted diaryl phosphoric acid.

In a single stage extraction, a separatory funnel mounted in a wristshaker is utilized. The aqueous acidic solution is an oxidized wetprocess phosphoric acid (WPA) obtained from a western phosphate depositand containing 1.53 grams per liter vanadium as V₂ O₅ and 0.148 gramsper liter uranium as U₃ O₈. The organic extractant phase is a kerosenediluent containing various quantities of tri-n-octylphosphine oxide(TOPO) and dioctylphenyl phosphoric acid (DOPPA) as set forth in Table Ibelow. The separatory funnel contains a portion of the organicextractant solution and is contacted with the oxidized wet processphosphoric acid. The organic to aqueous ratio is maintained at 1 and theextractions are conducted at 50° C. with a 20 minute mix time. After theextraction, the aqueous phase is analyzed to determine the percentvanadium and uranium remaining therein. The results are set forth inTable I below. Further, Table I also shows the percent of V₂ O₅ and U₃O₈ extracted.

                  TABLE I                                                         ______________________________________                                        SIMULTANEOUS EXTRACTING OF VANADIUM AND                                       URANIUM FROM OXIDIZED WPA BY VARIOUS                                          MOLE RATIOS OF DOPPA AND TOPO                                                 Solvent Composition                                                                         Analysis, g/l Percent                                           Molarity      Aqueous Phase Extracted                                         TOPO    DOPPA     V.sub.2 O.sub.5                                                                        U.sub.3 O.sub.8                                                                      V.sub.2 O.sub.5                                                                     U.sub.3 O.sub.8                       ______________________________________                                        0.2     0.1       0.71     0.058  46.4  60.8                                  0.2     0.15      1.07     0.048  30.1  67.6                                  0.2     0.2       1.42     0.045  7.2   69.6                                  0.2     0.3       1.42     0.036  7.2   75.7                                  0.3     0.15      0.59     0.039  61.4  73.6                                  0.25    0.125     0.62     0.052  59.5  64.9                                  0.20    0.0       0.31     0.142  79.7   4.1                                  0.0     0.2       1.44     0.136  5.9    8.1                                  ______________________________________                                    

From the results set forth in Table I, it will be seen that the optimumsimultaneous coextraction of uranium and vanadium occurs when the molarratio of alkyl substituted diaryl phosphoric acid to trialkylphosphineoxide is about 0.5. The exact concentration utilized depends on theconcentration of vanadium in the solution to be processed and on therelative economic value of the two metals compared with the total costsof the recovery process.

EXAMPLE II

This example more fully demonstrates the simultaneous coextractioncapability of this invention.

In a four-stage extraction process, four separatory funnels mounted inwrist shakers are utilized. The aqueous acidic solution is WPA obtainedfrom a western phosphate deposit containing 1.53 grams per litervanadium as V₂ O₅ and 0.148 grams per liter uranium as U₃ O₈. Theorganic extractant phase is a kerosene diluent containing 0.25 Mtri-n-octylphosphine oxide (TOPO) and 0.125 M dioctylphenyl phosphoricacid (DOPPA). Each of the four separatory funnels contains a portion ofthe organic extractant solution and is contacted serially with the WPA.The organic to aqueous ratio is maintained at 1 and the extractions areconducted at 50° C. with a 20 minute mix time per stage. After eachextraction stage, the aqueous phase is analyzed to determine the percentvanadium and uranium remaining therein. The results are set forth inTable II below.

                  TABLE II                                                        ______________________________________                                        SERIAL SIMULTANEOUS EXTRACTIONS OF                                            VANADIUM AND URANIUM FROM OXIDIZED WPA BY                                     0.125M DOPPA AND 0.25M TOPO SOLVENT                                                       Analysis, g/l  Cumulative Percent                                 Extraction Stage                                                                          Aqueous Phase  Extracted                                          #           V.sub.2 O.sub.5                                                                        U.sub.3 O.sub.8                                                                         V.sub.2 O.sub.5                                                                      U.sub.3 O.sub.8                         ______________________________________                                        1           0.57     0.050     62.7   66.2                                    2           0.38     0.015     75.2   89.9                                    3           0.28     0.005     81.7   96.6                                    4           0.26     0.001     83.0   99.3                                    ______________________________________                                    

EXAMPLE III

This example illustrates the preferential separation of vanadium from avanadium-uranium loaded extractant organic phase.

A sample of organic extract phase loaded with vanadium and uranium isprepared containing 0.25 M tri-n-octylphosphine oxide (TOPO) and 0.125 Mdioctylphenyl phosphoric acid (DOPPA) in kerosene loaded with 2.61 gramsper liter V₂ O₅ and 0.175 grams per liter U₃ O₈.

The sample is scrubbed with water in a two-stage process. It has beenfound that an initial water scrub removes some of the impurities thatare coextracted from WPA, such as phosphoric acid and hydrofluoric acid.The removal of such impurities reduces the amount of sodium carbonate orother base required to strip the uranium and vanadium from the loadedextractant. The sample of loaded organic is serially contacted with anequal amount of water placed in separatory funnels mounted on a wristaction shaker and agitated for 5 minutes at a temperature of 50° C.Following the water scrub, a sample of the aqueous phase of each stageis obtained and analyzed. The analyses are set forth in Table III below.

                  TABLE III                                                       ______________________________________                                        WATER SCRUBBING OF VANADIUM                                                   AND URANIUM LOADED                                                            0.125 DOPPA and 0.25 TOPO SOLVENT                                                      Analysis of Scrub                                                                            Analysis of Scrubbed                                  Scrub Stage                                                                            Water, g/l     Organic Phase, g/l                                    #        V.sub.2 O.sub.5                                                                         U.sub.3 O.sub.6                                                                        V.sub.2 O.sub.5                                                                       U.sub.3 O.sub.8                           ______________________________________                                        1        0.17      <0.001   --      --                                        2        0.07      <0.001   2.32    0.175                                     ______________________________________                                    

The results set forth in Table III clearly show that substantially nouranium and little vanadium is removed by water scrubbing.

The water scrubbed organic extract phase preferentially is stripped ofits vanadium content utilizing the following procedure. In the firststeps, the water scrubbed loaded organic extract phase is placed in abeaker equipped with a stirrer. A sufficient volume of an aqueous sodiumcarbonate strip solution is slowly added to the beaker to provide anequilibrium pH of about 6.0. The contents of the beaker then are stirredfor 5 minutes at 50° C. following which the aqueous strip solutioncontaining the vanadium is removed from the beaker. That solution andthe remaining organic extract phase both are analyzed. The results areset forth in Table IV below. In the second stage of stripping, theremaining organic extract phase is contained with a further solution ofsodium carbonate in an amount sufficient to provide an equilibrium pH of8.4. The mixture is stirred for 5 minutes at 50° C. following which theaqueous strip solution containing residual vanadium is recovered. Thatsolution and the then remaining organic phase are analyzed. The resultsare set forth in Table IV below.

                  TABLE IV                                                        ______________________________________                                        SELECTIVE STRIPPING OF VANADIUM                                               FROM VANADIUM AND URANIUM LOADED                                              0.125M DOPPA AND 0.25M TOPO SOLVENT                                           Analysis of Vanadium-                                                         Containing Strip     Analysis of Stripped                                     Solution, g/l        Organic Phase, g/l                                       Stage No.                                                                              V.sub.2 O.sub.5                                                                       U.sub.3 O.sub.8                                                                       pH    V.sub.2 O.sub.5                                                                       U.sub.3 O.sub.8                        ______________________________________                                        0       --       --      --    2.32    0.175                                  1       2.14     <0.001  6.0   0.17    0.182                                  2       0.06     <0.001  8.4   <0.05   0.184                                  ______________________________________                                    

The results as set forth in Table IV clearly demonstrate that thevanadium is recovered substantially free of uranium. Less than 0.001grams per liter uranium are found with the vanadium. The uraniumsubsequently is recovered from the vanadium stripped extractant bycontacting it with a sufficient amount of an aqueous base solution tomaintain the equilibrium pH above about 8.4.

Alternatively, both the uranium and vanadium may be stripped by areducing agent in acid solution, or the uranium alone may be stripped bya reducing agent in acid solution or by high concentration of phosphoricor hydrofluric acid. For example, the vanadium stripped organic extractphase is stripped of its uranium utilizing the following procedure. Theuranium loaded organic is contacted with an equal amount of alternatestripping agent aqueous solution placed in separatory funnels mounted ona wrist-action shaker and agitated for 5 minutes at a temperature of 50°C. The organic and aqueous phases are separated and the organic phase isanalyzed. The results of these tests are set forth in Table V below.

                  TABLE V                                                         ______________________________________                                        SINGLE STAGE STRIPPING OF URANIUM FROM                                        VANADIUM STRIPPED-URANIUM LOADED                                              0.125M DOPPA AND 0.25M TOPO SOLVENT                                                            Analysis of Stripped                                         Stripping Agent  Organic Phase, g/l                                           (In H.sub.2 O)   U.sub.3 O.sub.8                                              ______________________________________                                        NONE             0.184                                                        85% H.sub.3 PO.sub.4                                                                           0.009                                                        12M H.sub.3 PO.sub.4 *                                                                         0.028                                                        20% HF           0.040                                                        ______________________________________                                         *Containing 2 g/l iron (II)                                              

EXAMPLE IV

This example illustrates the preferential separation of vanadium from avanadium-uranium loaded extractant organic phase using an aqueous acidicstripping solution containing a reducing agent.

A sample of organic extract phase loaded with vanadium and uranium isprepared and scrubbed with water as illustrated in Example III. Thewater scrubbed organic extract phase contains 0.25 Mtri-n-octylphosphine oxide (TOPO) and 0.125 M dioctylphenyl phosphoricacid (DOPPA) in kerosene loaded with 1.0 grams per liter V₂ O₅ and 0.081grams per liter U₃ O₈.

The water scrubbed organic extract phase preferentially is stripped ofits vanadium content utilizing the following procedure. The sample iscontacted with an equal volume of a sulfuric acid solution containingferrous iron placed in a separatory funnel mounted on a wrist-actionshaker and agitated for 5 minutes at a temperature of 50° C. Followingthe agitation, the organic and aqueous phases are separated and theaqueous phase is analysed. The results of this test are set forth inTable VI below.

                  TABLE VI                                                        ______________________________________                                        SELECTIVE STRIPPING OF VANADIUM FROM                                          VANADIUM AND URANIUM LOADED                                                   0.125M DOPPA - 0.25M TOPO SOLVENT                                                     Analysis of Vanadium                                                                         Analysis of                                                    and Uranium Loaded                                                                           Resultant Strip                                                Organic Phase, g/l                                                                           Solution, g/l                                          Stripping Agent                                                                         V.sub.2 O.sub.5                                                                         U.sub.3 O.sub.8                                                                          V.sub.2 O.sub.5                                                                      U.sub.3 O.sub.8                         ______________________________________                                        5 vol. % H.sub.2 SO.sub.4 *                                                             1.0       0.081      0.76   0.0019                                  ______________________________________                                         *containing 9 g/l iron II                                                

The results as set forth in Table VII clearly demonstrate that thevanadium is recovered substantially free of uranium. Less than 0.002grams per liter uranium are found with the vanadium.

EXAMPLE V

This example illustrates the preferential separation of vanadium from avanadium-uranium loaded extractant organic phase using aqueous nitricacid solutions.

A sample of organic extract phase loaded with vanadium and uranium isprepared and scrubbed with water as illustrated in Example III. Thewater scrubbed organic extract phase contains 0.25 Mtri-n-octylphosphine oxide (TOPO) and 0.125 M dioctylphenyl phosphoricacid (DOPPA) in kerosene loaded with 1.0 grams per liter V₂ O₅ and 0.081grams per liter U₃ O₈.

The water scrubbed organic extract phase preferentially is stripped ofits vanadium content utilizing the following procedure. Samples arecontacted with an equal volume of a nitric acid solution placed inseparatory funnels mounted on a wrist-action shaker and agitated for 5minutes at a temperature of 50° C. Following the agitation, the organicand aqueous phases are separated and the aqueous phase is analyzed. Theresults of these tests are set forth in Table VII below.

                  TABLE VII                                                       ______________________________________                                        SELECTIVE STRIPPING OF VANADIUM FROM                                          VANADIUM AND URANIUM LOADED                                                   0.125M DOPPA - 0.25M TOPO SOLVENT                                                     Analysis of Vanadium                                                                        Analysis of                                                     and Uranium Loaded                                                                          Resultant Strip                                                 Organic Phase, g/l                                                                          Solution, g/l                                           Stripping Agent                                                                         V.sub.2 O.sub.5                                                                         U.sub.3 O.sub.8                                                                         V.sub.2 O.sub.5                                                                       U.sub.3 O.sub.8                         ______________________________________                                        0.5M HNO.sub.3                                                                          1.0       0.081     0.24    <0.0005                                 0.5M HNO.sub.3 +                                                              3M NH.sub.4 NO.sub.3                                                                    1.0       0.081     0.37    <0.0005                                 1.0M HNO.sub.3                                                                          1.0       0.081     0.40    <0.0005                                 ______________________________________                                    

The results set forth in Table VII clearly demonstrate that the vanadiumis recovered substantially free of uranium. Further, the data show thatnitric acid solutions supplemented with additional nitrate salts andstronger nitric acid solutions improve vanadium stripping.

EXAMPLE VI

This example illustrates simultaneous aqueous acidic solution strippingof vanadium and uranium from a vanadium-uranium loaded extractantorganic phase.

A sample of organic extract phase loaded with vanadium and uranium isprepared and scrubbed with water as illustrated in Example III. Thewater scrubbed organic extract phase contains 0.25 Mtri-n-octylphosphine oxide (TOPO) and 0.25 M dioctylphenyl phosphoricacid (DOPPA) in kerosene loaded with 1.0 grams per liter V₂ O₅ and 0.081grams per liter U₃ O₈.

The water scrubbed organic extract phase simultaneously is stripped ofits vanadium and uranium by utilizing the following procedure. Samplesare contacted with equal volumes of aqueous acidic solutions placed inseparatory funnels mounted on a wrist-action shaker and agitated for 5minutes at a temperature of 50° C. Following the agitation, the organicand aqueous phases are separated and the aqueous phase is analyzed. Theresults of these tests are set forth in Table VII below.

                  TABLE VIII                                                      ______________________________________                                        SIMULTANEOUS VANADIUM                                                         AND URANIUM STRIPPING                                                         FROM VANADIUM AND URANIUM LOADED                                              0.125M DOPPA - 0.25M TOPO SOLVENT                                                     Analysis of Vanadium                                                                        Analysis of                                                     and Uranium Loaded                                                                          Resultant Strip                                                 Organic Phase, g/l                                                                          Solution, g/l                                           Stripping Agent                                                                         V.sub.2 O.sub.5                                                                         U.sub.3 O.sub.8                                                                         V.sub.2 O.sub.5                                                                      U.sub.3 O.sub.8                          ______________________________________                                        50% H.sub.3 PO.sub.4                                                                    1.0       0.081     0.49   0.091*                                   70% H.sub.3 PO.sub.4                                                                    1.0       0.081     0.49   0.078                                    85% H.sub.3 PO.sub.4                                                                    1.0       0.081     0.49   0.062                                    24% HF    1.0       0.081     0.94   0.087*                                   ______________________________________                                         *value is within the experimental accuracy of the fluorometric analysis       employed                                                                 

The results as set forth in Table VIII clearly demonstrate the abilityto simultaneously recover substantial amounts of vanadium and uraniumfrom a loaded organic extract phase.

EXAMPLE VII

This example illustrates simultaneous aqueous acidic solution strippingof vanadium and uranium from a vanadium-uranium loaded extractantorganic phase.

A sample of organic extract phase loaded with vanadium and uranium isprepared containing 0.25 M tri-n-octylphosphine oxide (TOPO) and 0.125 Mdioctylphenyl phosphoric acid (DOPPA) in kerosene loaded with 3.60 gramsper liter V₂ O₅ and 0.073 grams per liter U₃ O₈.

The loaded organic phase is stripped by contacting with an equal volumeof an aqueous acidic solution placed in a separatory funnel mounted on awrist-action shaker and agitated for 5 minutes at a temperature of 50°C. Following the agitation, the organic and aqueous phases are separatedand the aqueous phase is analyzed. The results of these tests are setforth in Table IX below.

                  TABLE IX                                                        ______________________________________                                        SIMULTANEOUS VANADIUM                                                         AND URANIUM STRIPPING                                                         FROM VANADIUM AND URANIUM LOADED                                              0.125M DOPPA - 0.25M TOPO SOLVENT                                                     Analysis of Vanadium                                                                        Analysis of                                                     and Uranium Loaded                                                                          Resultant Strip                                                 Organic Phase, g/l                                                                          Solution, g/l                                           Stripping Agent                                                                         V.sub.2 O.sub.5                                                                         U.sub.3 O.sub.8                                                                         V.sub.2 O.sub.5                                                                      U.sub.3 O.sub.8                          ______________________________________                                        85% H.sub.3 PO.sub.4                                                                    3.60      0.073     0.82   0.076*                                   24% HF    3.60      0.073     3.51   0.066                                    ______________________________________                                         *value is within the experimental accuracy of the fluorometric analysis       employed                                                                 

The results set forth in Table IX demonstrate an ability tosimultaneously strip vanadium and uranium from the loaded organic phase.

EXAMPLE VIII

This example illustrates the simultaneous aqueous acidic solutionstripping of vanadium and uranium from a vanadium-uranium loadedextractant organic phase.

A sample of organic extractant phase loaded with vanadium and uranium isprepared and scrubbed with water as illustrated in Example III. Thewater scrubbed organic extract phase contains 0.25 Mtri-n-octylphosphine oxide (TOPO) and 0.125 M dioctylphenyl phosphoricacid (DOPPA) in kerosene loaded with 0.49 grams per liter V₂ O₅ and0.090 grams per liter U₃ O₈.

The water scrubbed organic extract phase simultaneously is stripped ofits vanadium and uranium by utilizing the following procedure. Samplesare contacted with equal volumes of aqueous acidic solutions containinga reducing agent placed in separatory funnels mounted on a wrist-actionshaker and agitated for 5 minutes at a temperature of 50° C. Followingthe agitation, the organic and aqueous phases are separated and theaqueous phase is analyzed. The results of these tests are set forth inTable X, below.

                  TABLE X                                                         ______________________________________                                        SIMULTANEOUS VANADIUM                                                         AND URANIUM STRIPPING                                                         FROM VANADIUM AND URANIUM LOADED                                              0.125M DOPPA - 0.25M TOPO SOLVENT                                                       Analysis of Vanadium                                                                          Analysis of                                                   Uranium Containing                                                                            Resultant Strip                                     Stripping Organic Phase, g/l                                                                            Solution, g/l                                        Agent*   V.sub.2 O.sub.5                                                                         U.sub.3 O.sub.8                                                                         V.sub.2 O.sub.5                                                                      U.sub.3 O.sub.8                          ______________________________________                                        50% H.sub.3 PO.sub.4                                                                    0.49      0.090     0.49   0.064                                    70% H.sub.3 PO.sub.4                                                                    0.49      0.090     0.54** 0.093**                                  85% H.sub.3 PO.sub.4                                                                    0.49      0.090     0.54** 0.094**                                  ______________________________________                                         *containing 2 g/l iron II                                                     **value is within the experimental accuracy of the fluorometric analysis      employed                                                                 

The results set forth in Table X demonstrate the ability tosimultaneously strip substantial amounts of vanadium and uranium fromthe loaded organic phase.

EXAMPLE IX

This example illustrates individual preferential stripping andseparation of vanadium and uranium from a vanadium-uranium loadedextractant organic phase.

An organic phase containing 0.4 M tri-n-octylphosphine oxide (TOPO) and0.2 M dioctylphenyl phosphoric acid (DOPPA) in kerosene continuously isloaded with vanadium and uranium in a small multistaged extractionmodule. The loaded organic extract phase then enters a multistagestripping module. Vanadium stripping and separation is accomplished inthe first stage of the stripping module using a controlled volume ofphosphoric acid solution that contains sufficient reducing agent toprovide the stoichiometric quantity required to reduce the vanadium (V)content of the organic phase to the quadravalent state. This permits thepreferential separation of vanadium and allows only a small quantity ofthe uranium to be stripped. The aqueous phase resulting from thestripping is quite rich in vanadium. The vanadium stripped organic phasethen proceeds into a two stage phosphoric acid scrubber. The scrubbingis utilized to limit the advancement of vanadium containing solutioninto the downstream uranium stripping section. Iron is dissolved in theresultant vanadium scrub aqueous phase to provide the aqueous strippingsolution employed in the first stage vanadium stripping section. In thismanner, any vanadium scrubbed from the organic phase is returned to thevanadium stripping section to facilitate recovery.

The vanadium stripped and scrubbed organic phase then proceeds into theuranium stripping section comprising the fourth stage in the strippingmodule. In the fourth stage, the vanadium stripped and scrubbed organicphase contacts a controlled volume of phosphoric acid which contains areducing agent in sufficient quantity to reduce any residual vanadium(V) and the uranium (VI) content to the lower vanadium (IV) and uranium(IV) states. It has been shown in the practice of this invention thatthe presence of the reducing agent in quantities in excess of thestoichiometric requirement is beneficial to uranium stripping. Theuranium and vanadium stripped organic phase then enters a two stagephosphoric acid scrubber. The scrubbing is utilized to prevent theadvancement of high grade uranium strip solution to the organic phaserecycle storage tank. The scrubber aqueous phase was separated and splitinto two portions. Iron was dissolved in one portion of the resultantaqueous phase to provide the aqueous stripping solution employed in thefourth stage uranium stripping section. The remaining portion of thescrubber aqueous was recycled as aqueous feed to the two-stage vanadiumscrubbers. In this manner, any vanadium or uranium that was scrubbedfrom the organic phase was caused to finally separate with the vanadiumor uranium stripping products.

The preferential vanadium and uranium stripping of the loaded organicphase described hereinabove, produced a vanadium strip product solutioncontaining in excess of 97 percent of the recoverable vanadium and auranium strip product solution containing more than 93 percent of therecoverable uranium.

In the particular test described above, a 70 percent phosphoric acidsolution was employed in all of the stages in the stripping module.Satisfactory phosphoric acid concentrations for this process are fromabout 20 percent to about 95 percent H₃ PO₄. However, the phase ratiosand number of stages required to effect stripping may change withvarying concentrations. In addition, different acid concentrations maybe used in different stages of the stripping module.

While this particular test employs iron as the reducing agent in theaqueous acidic solution, any reducing agent which is compatible withphosphoric acid and that is capable of reducing vanadium (V) and uranium(VI) to lower valence states can be used in this process.

While the present invention has been described with respect to preferredembodiments thereof, it will be understood, of course, that certainchanges may be made therein without departing from its true scope asdefined in the appended claims.

What is claimed is:
 1. A process for the simultaneous recovery ofuranium (VI) and vanadium (V) from an aqueous acidic solution containingthe same which comprises: contacting said solution in the presence of atleast about 0.25 mole fluoride per mole vanadium with an organicextractant phase comprising(a) a substantially water-immiscible organicdiluent; (b) an alkyl substituted diaryl phosphoric acid having theformula ##STR3## where R₁ and R₂ represent aryl radicals at least one ofwhich is substituted with an alkyl group and the total number of carbonatoms in the alkyl substituted diaryl phosphoric acid is at least 13 and(c) a trialkylphosphine oxide having the formula ##STR4## where R, R'and R" are alkyl radicals containing from 4 to 14 carbon atoms, wherebythe uranium and vanadium are preferentially coextracted into the organicphase and, recovering the uranium and vanadium containing organic phase;the alkyl substituted diaryl phosphoric acid and trialkylphosphine oxidebeing present in the organic extractant phase in an amount sufficient toprovide a molar ratio of alkyl substituted diaryl phosphoric acid totrialkyphosphine oxide of from 1:8 to 1:1.
 2. The process of claim 1wherein the ratio of alkyl substituted diaryl phosphoric acid totrialkyphosphine oxide is in the range of from 1:3 to 4:5.
 3. Theprocess of claim 1 wherein the concentration of trialkylphosphine oxidein the organic phase is in the range of from 0.05 molar to 1.0 molar. 4.The process of claim 1 wherein the trialkylphosphine oxide istri-n-octylphosphine oxide.
 5. The process of claim 1 wherein the alkylsubstituted diaryl phosphoric acid is dioctylphenyl phosphoric acid. 6.The process of claim 1 wherein the ratio of alkyl substituted diarylphosphoric acid to trialkylphosphine oxide is about 0.5.
 7. The processof claim 1 wherein the alkyl substituted diaryl phosphoric acid isdioctylphenyl phosphoric acid and the trialkylphosphine oxide istri-n-octylphosphine oxide.
 8. The process of claim 1 wherein theaqueous acidic solution is a wet process phosphoric acid.
 9. The processof claim 1 wherein the uranium and vanadium are stripped from therecovered organic phase with an aqueous base solution.
 10. The processof claim 1 wherein the recovered organic phase is contacted with theaqueous basic solution in an amount sufficient to maintain theequilibrium pH at from about 5.5 to 8.4, whereby the vanadiumpreferentially is stripped from the organic phase to leave avanadium-barren uranium containing organic phase.
 11. The process ofclaim 10 wherein the uranium-containing organic phase is contacted withan aqueous basic carbonate solution in an amount sufficient to maintainthe equilibrium pH above about 8.4 whereby the uranium is stripped fromthe organic phase and recovering the uranium substantially free ofvanadium.
 12. The process of claim 10 wherein the uranium-containingorganic phase is contacted with at least one acid selected from thegroup consisting of phosphoric acid and hydrofluoric acid in aconcentration sufficient to remove substantially all of the uranium fromthe organic phase.
 13. The process of claim 10 wherein theuranium-containing organic phase is contacted with a solution containing(i) a reducing agent and (ii) at least one acid selected from the groupconsisting of phosphoric acid and hydrofluoric acid to removesubstantially all of the uranium from the organic phase.
 14. The processof claim 1 wherein the trialkylphosphine oxide is tri-n-octylphosphineoxide present in an amount sufficient to provide a concentration in theorganic phase of from about 0.1 to about 0.5 molar and the alkylsubstituted diaryl phosphoric acid is dioctylphenyl phosphoric acid. 15.The process of claim 1 wherein the trialkylphosphine oxide istri-n-octylphosphine oxide present in an amount sufficient to provide aconcentration of from about 0.25 molar to about 0.45 molar and the alkylsubstituted diaryl phosphoric acid is dioctylphenyl phosphoric acidpresent in an amount sufficient to provide a concentration of from about0.125 molar to about 0.23 molar.
 16. The process of claim 1 wherein thevanadium containing organic phase is contacted with at least onesolution selected from the group consisting of nitric acid and nitricacid containing additional nitrate salts to remove a substantialquantity of the vanadium from the organic phase.
 17. The process ofclaim 1 wherein the vanadium containing organic phase is contacted withan aqueous solution containing (i) a reducing agent and (ii) sulfuricacid.
 18. The process of claim 17 wherein the solution contains sulfuricacid in a range of from about 5 percent to about 35 percent by weight.19. The process of claim 17 wherein the reducing agent is ferrous iron.20. The process of claim 1 wherein the vanadium containing organic phaseis contacted with an aqueous acidic solution containing a reducingagent.
 21. The process of claim 20 wherein the reducing agent is ferrousiron.
 22. The process of claim 1 wherein vanadium and uranium aresimultaneously stripped from the recovered organic phase by contactingwith at least one acid selected from the group consisting of phosphoricacid and hydrofluoric acid in a concentration sufficient to removesubstantially all of the vanadium and uranium from the organic phase.23. The process of claim 1 wherein the recovered organic phase iscontacted with a solution containing (i) a reducing agent and (ii) atleast one acid selected from the group consisting of phosphoric acid andhydrofluoric acid to remove substantially all of the vanadium from theorganic phase.
 24. The process of claim 23 wherein the reducing agent isferrous iron.
 25. The process of claim 23 wherein the reducing agent istrivalent vanadium.
 26. The process of claim 23 wherein the organicphase is contacted with the solution in at least two stages topreferentially remove vanadium from the organic phase and then removethe uranium be contacting the organic phase with additional quantitiesof the solution.
 27. The process of claim 1 wherein the aqueous acidicsolution is wet process phosphoric acid containing at least one memberselected from the group consisting of yttrium, iron, zinc and bromine.28. The process of claim 27 wherein the organic phase also extracts themember selected from the group consisting of yttrium, iron, zinc andbromine.
 29. The process of claim 28 wherein the member selected fromthe group consisting of yttrium, iron, zinc and bromine is stripped fromthe recovered organic phase with an aqueous acidic solution.
 30. Theprocess of claim 1 wherein the recovered organic phase is contacted witha solution containing (i) a reducing agent and (ii) at least one acidselected from the group consisting of phosphoric acid and hydrofluoricacid to remove substantially all of the uranium from the organic phase.